The clinical interface between immunology, hematology, and oncology has long been appreciated. Many conditions treated by the hematologist or oncologist have either an autoimmune or immunodeficient component to their pathophysiology that has led to the widespread adoption of immunosuppressive medications by hematologists, whereas oncologists have sought immunologic adjuvants that might enhance endogenous immunity to tumors. To date, these interventions have generally consisted of nonspecific modes of immunosuppression and immune stimulation. In addition to the limited efficacy of these interventions, toxicities secondary to their nonspecificity have also limited their overall success. Therefore, alternative strategies have been sought.
Elucidation of the functional role of a rapidly increasing number of cell surface molecules has contributed greatly to the integration of immunology with clinical hematology and oncology. Nearly 200 cell surface antigens have been identified on cells of the immune and hematopoietic systems (Schlossman S F, Boumsell L, Gilks J M, Harlan T, Kishimoto, C Morimoto C, Ritz J., Shaw S, Silverstein R L, Springer T A, Tedder T F, Todd RF:CD antigens (1993), Blood 83:879, 1994). These antigens represent both lineage-restricted and more widely distributed molecules involved in a variety of processes, including cellular recognition, adhesion, induction and maintenance of proliferation, cytokine secretion, effector function, and even cell death. Recognition of the functional attributes of these molecules has fostered novel attempts to manipulate the immune response. Although molecules involved in cellular adhesion and antigen-specific recognition have previously been evaluated as targets of therapeutic immunologic intervention, recent attention has focused on a subgroup of cell surface molecules termed costimulatory molecules (Bretscher P: “The two-signal model of lymphocyte activation twenty-one years later.” Immunol. Today 13:73, (1992); Jenkins M K, Johnson J G: “Molecules involved in T-cell co-stimulation.” Curr Opin Immunol 5:351, (1993); Geppert T, Davis L. Gur H. Wacholtz M. Lipsky P: “Accessory cell signals involved in T-cell activation.” Immunol Rev 117:5, (1990); Weaver C T, Unanue E R: “The co-stimulatory function of antigen-presenting cells.” Immunol Today 11:49, (1990); Stennam R M, Young J W: “Signals arising from antigen-presenting cells.” Curr Opin Immunol 3:361, (1991)).
Co-stimulatory molecules do not initiate but rather enable the generation and amplification of antigen-specific T-cell responses and effector function (Bretscher P: “The two-signal model of lymphocyte activation twenty-one years later.” Immunol. Today 13:73, (1992); Jenkins M K, Johnson J G: Molecules involved in T-cell co-stimulation.” Curr Opin Immunol 5:351, (1993); Geppert T, Davis L. Gur W. Wacholtz M. Lipsky P: “Accessory cell signals involved in T-cell activation.” Immunol Rev 117:5, (1990); Weaver C T, Unanue E R: “The co-stimulatory function of antigen-presenting cells.” Immunol Today 11:49, (1990); Stennam R M, Young J W: “Signals arising from antigen-presenting cells.” Curr Opin Immunol 3:361, (1991); June C H Bluestone J A, Linsley P S I Thompson C D: “Role of the CD28 Receptor in T-cell activation.” Immunol. Today 15:321, (1994)).
Recently, one specific co-stimulatory pathway termed B7:CD28 has been studied by different research groups because of its significant role in B and T cell activation (June C H, Bluestone J A, Linsley P S, Thompson C D: “Role of the CD28 receptor in T-cell activation.” Immunol Today 15:321, (1994); June C H Ledbetter J A: “The role of the CD28 receptor during T-cell responses to antigen.” Annu Rev Immunol 11:191, (1993); Schwartz RH: “Co-stimulation of T lymphocytes: The role of CD28, CTLA-4, and B7/BB1 in interleukin-2 production and immunotherapy.” Cell 71:1065-1068, (1992); Jenkins M K, Taylor P S, Norton S D, Urdahl K B: “CD28 delivers a costimulatory signal involved in antigen-specific IL-2 production by human T cells. Journal of Immunology 147:2461-2466 (1991). Since this ligand:receptor pathway was discovered four years ago, a large body of evidence has accumulated suggesting that B7:CD28 interactions represent one of the critical junctures in determining immune reactivity versus anergy (June C H, Bluestone J A, Linsley P S, Thompson C D: “Role of the CD28 receptor in T-cell activation.” Immunol Today 15:321, (1994); June C H, Ledbetter J A: “The role of the CD28 receptor during T-cell responses to antigen.” Annu Rev Immunol 11:191, (1993); Schwartz R H: “Co-stimulation of T lymphocytes: The role of CD28, CTLA-4, and B7/BB1 in interleukin-2 production and immunotherapy.” Cell 71:1065-1068, (1992); Cohen J: “Mounting a targeted strike on unwanted immune responses” (news; comment). Science 257:751, (1992); Cohen J: “New protein steals the show as ‘co-stimulator’ of T cells” (news; comment). Science 262:844, (1993)).
In particular, the role of the human B7 antigens, i.e., human B7.1 (CD80) and B7.2 (CD86), has been reported to play a co-stimulatory role in T-cell activation. See, e.g., Gimmi C D, Freeman, G J, Gribben J G, Sugita K, Freedman A S, Morimoto C, Nadler L M: “B-cell surface antigen B7 provides a costimulatory signal that induces T cells to proliferate and secrete interleukin 2.” Proc. Natl. Acad. Sci. (USA) 88:6575-6579 (1991).